Of mice and mines: trained rats search for explosives, tuberculosis

According to the International Campaign to Ban Landmines, an estimated
15-20,000 people are killed by landmines each year. Detecting those
mines—without setting them off—is a dilemma that faces many post-conflict
regions of the world. But Bart Weetjens may have found a six-pound solution
to the problem: the African giant pouched rat. Working for APOPO, a Belgian organization founded to
explore the idea, Weetjens has successfully trained rats to locate land
mines by smell. The animals have also been trained to identify tuberculosis
from samples, a development that may prove equally promising.

How did he come up with the idea of using rats for these detection problems? In a Skype interview from his office in Tanzania, Weetjens confessed that he's always been interested in helping Africa but was initially stalled for solutions. "I wanted to do something in the real world, something appropriate to the environment," he told Ars.

In the early 1990's, when it became a cause célèbre for Princess Diana and others, Weetjens began looking into landmines. In travels to Mozambique and Angola, he watched as trained dogs searched for buried explosives. But dogs are expensive (in the neighborhood of $25,000), and many were lost to disease or the mines they were meant to detect. There had to be a better way.

The breakthrough came when Weetjens saw an article in which gerbils had been trained as a "black box" vapor detector. He knew that those rodents couldn't be his choice: "way too nervous… but rats could do the job." After searching for grant money for more than two years, he was able to begin breeding tame pouched rats (a hardy, adaptable African species) for training. Beginning with a stock of thirty animals, APOPO has now trained more than 120 free-running "Hero Rats," twenty-three of which are certified by an international agency as equal to dogs in effectiveness.

The similarities don't actually end at the certification. Like dogs, some rats can be easier to train than others. On average, the rats take 10-12 months to be fully trained for mine-sniffing, Weetjens said, a process that's complicated by the distracting stimulus of the outside environment. The rats are trained using a clicker and a banana reward (again, much like dogs, except for the fruit), and they've had a graduation rate of about one out of every four "students."

Successfully trained rats indicated the location of mines by pointing their noses directly at the ground for more than five seconds. "That's a very long time for a rat," noted Weetjens, although he added that some also develop circling or scratching behavior as an indicator. The rodents wear harnesses and run along strings laid out across the suspected area, ensuring that they cover the entire grid. And at six pounds, they're too light to set off the explosives by accident.

A mine-detecting rat working its grid

As exciting as this may be, Weetjens also sees a great deal of promise in the newer tuberculosis detection research. Tuberculosis-sniffing rats have substantial logistical advantages over traditional techniques. In preliminary tests, a pair of the animals were able to detect 86 percent of infected TB samples, with a 10 percent false-positive rate. Clearly, they won't replace a full lab for accuracy, but the rats are able to check 40 samples in only seven minutes—a task that would take an entire day for a technician.

Weetjens hopes that they can be used as a portable screening tool, one that can be located near slums and other at-risk areas. The disease kills about 1.6 million people per year, according to the World Health Organization. And since many tuberculosis cases in Africa accompany HIV, a fast screening technique is a perfect opportunity to educate patients about the disease.

What's the future for these not-so-stupid pet tricks? Weetjens isn't ruling out new directions, including commercial applications—sustainable funding for testing with rats (as opposed to testing on rats) isn't easy to find. But his ultimate aim remains humanitarian: Recent research into diagnosing cancer with animals is one possibility, as are "rescue rats"—the rodents are small and light enough to slip into collapsed structures in search of trapped occupants. And for right now, Weetjens seems pretty happy with the progress of his own personal rat race.